Derrick apparatus

ABSTRACT

A derrick apparatus for a drilling machine ( 10 ), the apparatus comprising a fixed structure ( 48, 50 ) for supporting drill equipment ( 14, 16 ), wherein the fixed structure ( 48, 50 ) has a generally prismatic shape with a generally constant cross-section along the vertical extent of the fixed structure ( 48, 50 ), and wherein the fixed structure ( 48, 50 ) comprises supporting beams ( 48, 50 ) about outer parts of the fixed structure and a void extending across the internal width of the fixed structure ( 48, 50 ).

The present invention relates to a derrick structure, for example a derrick used for well operations.

Drilling derricks have had similar designs for the last 70-80 years. Most designs utilise a lattice work construction of beams to form a tower or pylon that supports the drilling equipment. Derricks are used on land, on offshore oil platforms and rigs and also on drill ships, which are typically equipped with a derrick mounted over a moon pool. The design of a traditional derrick structure uses a bolted steel construction forming a lattice-work frame, typically in a square pylon or tower shape. A “V-door” at the base of the derrick is left open, without obstruction from a cross-beam or other structural member. This is used to permit the drill string and pipes to be taken up into the space inside the derrick.

Rigs such as semi-submersible rigs and jack-up rigs can be specially designed structures or adapted barges. They are towed to the drilling site, where they are anchored or jacked up on the seabed. A derrick positioned above a moon pool in the deck of the rig is used for drilling operations.

Drillships can be existing ship designs retro-fitted with drilling apparatus, or they may be ships with a hull and structure that is specially designed for drilling operations. Drillships are typically used for exploratory drilling of new oil or gas wells offshore and in deep water. A drillship may also be used as a platform to carry out well maintenance or completion work such as casing and tubing installation or subsea “Christmas Tree” (manifold and blow-out preventer) installations. Drillships are completely independent and are able to drill in deep water (depths in excess of 2500 metres). This provides advantages compared to fixed platform structures and less independent mobile solutions such as semi-submersibles and jack-up rigs. A drillship can sail relatively quickly between sites and perform drilling operations without the need for other vessels.

The sailing time and set-up time when the drillship or rig is not drilling is effectively a cost for the operator. For information, at the time of filing a very rough daily rate for an operating drilling unit is about 1 M$/day, and when the drilling unit is not operating an rough estimation of the loss incurred to the owner when the unit is sailing is in the order of 0.5 M$/day. Steps are taken to minimise sailing time by taking efficient routes between drilling sites in order to minimise the losses during times of non-operation. A conflict arises between sailing time and set-up time when the ship is required to pass through shipping routes with fixed height bridges, such as the Panama Canal, the Suez Canal and the Bosphorus Strait. These routes are constrained by the air draft available to shipping due to the height of road bridges, such as the Bridge of the Americas over the Panama Canal entrance, the Suez Canal Bridge (also known as the Shohada 25 January Bridge) and the Bosphorus Bridge. Of the three, the Bosphorus Bridge has the least clearance and gives rise to a height limit of 58 metres above the waterline for vessels to be able to pass beneath the bridge freely. A higher limit is possible with special preparations, and at present this maximum height limit is 62 metres.

Since the clearance beneath these bridges is less than the usual height required for a derrick on a drillship or rig then it is often necessary for the derrick to be deconstructed to permit the ship or rig to use those routes. The additional time for disassembly and reassembly of the derrick and drill equipment, re-commissioning the reassembled structure and equipment and testing after commissioning can be several months. The time and cost associated with disassembly and reassembly/re-commissioning is less than the journey time and associated costs for an alternative route that avoids the height restriction and so operators routinely carry out such disassembly and reassembly/re-commissioning. However, the time lost to disassembly and reassembly/re-commissioning and also the costs are still considerable, and hence it is clearly desirable to reduce the time and cost involved in traversing height restricted shipping routes.

Collapsible or height adjustable derrick structures have been developed to address this issue. For example, KR 10-2010-0004898 describes a derrick with a hinged top part, wherein the top part can fold over to the side(s) of the derrick either in one piece or split in two. Also, US 2010/176079 discloses a derrick where the upper section, which supports the crown block, can be folded sideways or retracted on jacks in order to reduce the total height. The derricks of KR 10-2010-0004898 and US 2010/176079 are both of the bolted steel construction described above.

Viewed from a first aspect the present invention provides a derrick apparatus for drilling operations, the apparatus comprising: a fixed structure for supporting fixed drill equipment such as a pipe racker; and a folding top structure having an erected position and a folded position, wherein when in the erected position the top structure is for supporting a top drive drilling machine and wherein at least a part of the top structure is arranged to fold around and/or beside a part of the fixed drill equipment on the fixed structure such that when the top structure is in the folded position the height of the derrick may be reduced to the height of the fixed drill equipment without disturbing the fixed drill equipment.

With this arrangement the derrick apparatus folds down to the height of the fixed drill equipment without the need to disturb the equipment so the fixed drill equipment mounted on the fixed structure does not need to be moved or disassembled. The term ‘fixed drill equipment’ as used herein refers to drill equipment that is typically mounted and fixed in place on a static part of a derrick. Such fixed equipment may comprise the pipe racker, associated pipe handling arms and the fingerboards. This fixed equipment is to be contrasted with parts of the drill equipment that are not fixed but instead are movably supported on cables and/or rails. The non-fixed equipment may include the top drive drilling machine and travelling block. The folding structure is hence designed such that it can be moved from the erected position to the folded position without being obstructed by the fixed drill equipment mounted on the fixed structure. This is highly beneficial since the fixed drill equipment is complex and requires alignment when it is installed. Since the fixed drill equipment is not disturbed there is no need for it to be disassembled or moved in any way when the top structure is folded, as a consequence it is not necessary to reassemble and re-commission the drill equipment when the folding derrick is folded and unfolded. This leads to considerable efficiency gains compared to conventional bolted derrick structures. In preferred embodiments the derrick comprises the fixed drill equipment mounted on the fixed structure and thus the derrick may comprise one or more of the pipe racker, associated pipe handling arms and the fingerboards, with the at least a part of the top structure being arranged to fold around and/or beside a part of this fixed drill equipment. The fixed structure may also preferably include drawworks and dead line anchors, utility winches and so on.

The top drive of the drill machine and related parts will necessarily be affected by the folding of the structure, but these parts are not fixed in place nor mechanically aligned. Instead they are movably supported by cable and guide rails. The top drive may therefore be easily moved down and secured on its regular guide rails at a point beneath the folded height of the folding structure and it can be raised again equally easily. No fixed equipment is disturbed. In preferred embodiments, the top drive is lowered on its guide rails and secured above the drill floor. Then the upper part of the guide rails may be disconnected and lowered with guidance from the remaining guide rails below and secured above the top drive.

With the arrangement of this aspect of the invention the maximum height of the derrick apparatus can be reduced down to the height of the fixed drill equipment on the fixed structure, since the folding structure folds down around and/or beside the drill equipment. In the prior art folding structures of KR 10-2010-0004898 and US 2010/176079 the folding structures fold over and remain above the drill equipment height. Also, in the arrangement disclosed in US 2010/176079 that makes use of a retractable top structure, it is necessary for space to be provided above the fixed drill equipment for the top structure to move into. Hence, the present arrangement is advantageous over these known height adjusting derricks since it can reduce the height of the derrick right down to the drill equipment height. Clearly this provides the smallest height for the derrick for a given drill string handling capability (i.e. for a given height of drill equipment) without requiring disassembly of the fixed drill equipment.

The derrick apparatus may be arranged to fold down to a maximum height of less than 60 metres, preferably less than 55 metres, more preferably less than 52 metres. The Bridge of the Americas has a clearance of 61.3 metres at high tide and the Bosphorus Bridge has a maximum clearance of 64 metres, with a maximum height for free passage of 58 metres. The air draft of the ship will be made up of the height of the derrick apparatus (from deck level) and the draft of the ship. By having a folding arrangement that folds down to the heights set out above the derrick apparatus can be made small enough for a ship or other floating structure to pass beneath the these bridges and similar bridges.

In a preferred embodiment, the folding structure comprises an arrangement of two or more hinged beams, for example box beams or girders, wherein there is a void between two beams. For example, a void may be created by the absence of cross-members or struts between the beams. This enables efficient folding of the beams toward each other and/or about or beside the drill equipment since during the folding operation the void or multiple voids can be used to provide space for parts of the folding structure, to enable the folding structure to move close to the fixed structure and/or to permit parts of the folding structure to be placed around or beside the fixed drill equipment.

The folding structure may comprise two beams that fold to two sides of the fixed drill equipment with a void between these beams. In this case the two beams are placed around the fixed drill equipment and the drill equipment occupies the void. This enables the beams to fold down to the fixed drill equipment height or below without disturbing the fixed drill equipment.

Alternatively or in addition the folding structure may comprise beams that are rotatably connected to one another, by hinges for example, and a void that is in between those beams when the folded structure is erect. This void may enable the rotatably connected beams to fold close together without hindrance. Preferably the void is utilised to enable the rotatably connected beams to fold apart and to fit around parts of the fixed structure when the folding top structure is in the folded position. Since there is a space between the beams there are no parts that prevent the beams from being placed close to parts of the fixed structure.

When in the erected position the folding top structure preferably includes a generally triangular shape in side view, with the sides of the triangle being formed by two beams of the top structure and a part or parts of the fixed structure and vertices of the triangle being formed at the two points where the two beams connect to the fixed structure and a point where the two beams connect to each other.

A part or part(s) of the folding structure are preferably movably connected to the fixed structure at the height of the highest part of the fixed drill equipment or below that height. With this arrangement the parts can be folded toward or away from the fixed drill equipment and down to a height that is the same as or below the fixed drill equipment height. The connection may be via a mechanism arranged for rotating movement of the part of the folding structure relative to the fixed structure, for example by means of a hinge. The connection may alternatively or additionally be by means of a joint arranged for a sliding connection of the part of the folding structure relative to the fixed structure. A part or parts of the folding structure may be connected to the fixed structure for both rotational and sliding movement.

The derrick apparatus preferably includes an actuator mechanism for folding and/or unfolding the foldable top structure. The actuator mechanism may comprise one or more winch, gear mechanism, hydraulic actuator or other suitable device. In a preferred embodiment the actuator mechanism is a winch attached to a point on a rotatable member of the folding structure.

In a preferred arrangement, the folding structure comprises a part rotatably connected to the fixed structure at an outer portion of the fixed structure and arranged to fold inwardly over the fixed structure.

The folding top structure may comprise a first part with a rotating connection to the fixed structure and a second part with a rotating connection to the first part. Preferably, the second part is rotatably connected to the first part at a point spaced from the rotating connection of the first part to the fixed structure. The second part may be releasably connected to the fixed structure at a point spaced from the rotating connection of the second part to the first part. Preferably, the connection of the first part and the second part is at an upper location on the top structure when it is in the erected position. The connection between the first part and the second part may form a mounting point for the crown block and/or for the top drive drill machine in the erected position. When folded, the first part may fold down around or beside a part of the fixed drill equipment and the second part may be released from the releasable connection and folded down beside the fixed structure or atop the first part.

In a particularly preferred embodiment the folding top structure comprises a frame rotatably connected at a first point to a first side of the fixed structure with an inclined beam rotatably connected to the frame at a second point spaced away from the first point and the inclined beam releasably connected to the fixed structure at a third point spaced away from the second point and the first point. With this arrangement when in the erected position the folding top structure may include a generally triangular shape in side view, with the sides of the triangle being formed by the frame, the inclined beam and a part or parts of the fixed structure extending between the first point and the third point. The frame may be an A-frame and preferably includes a void enabling it to fold over and about a part of the fixed drill equipment on the fixed structure. The inclined beam preferably slides down a side of the fixed structure when the folding structure is moved to its folded position. The folding operation may be controlled by a winch or gear mechanism arranged to lift the frame from the folded position toward the erected position. In a preferred arrangement the frame extends beyond the first point in a direction away from the second point, and the folding operation is controlled by a winch attached to the frame at a fourth point on the frame that is spaced away from the first point in the direction away from the second point.

The inclined beam may be a single beam. Since the beam slides away along a side of the fixed structure it is not obstructed by the drill equipment and does not need to fit about or beside the equipment. However, in alternative arrangements the inclined beam may be multiple beams forming a frame, such as a second A-frame that opposes the first A-frame mentioned above. This could allow both parts of the top structure to be placed around drill equipment or parts of the fixed structure. In other alternative arrangements the inclined beam may be joined at the second and third points in a different manner, for example with a rotating connection to the fixed structure at the third point and a releasable connection to the frame at the second point. With this arrangement the inclined beam and/or the frame could be folded away down the side of the fixed structure in the folded configuration.

The folding top structure may provide an offset drill centre. Thus, the mounting point for the crown block and/or drill line, which may be a coupling point of parts of the structure and/or a vertex of a triangular shape formed by the structure, may be offset from the centre of the fixed structure. This offset arrangement can advantageously enable more space for the driller's cabin and/or ancillary parts to be mounted in the fixed structure beside the main drill line. In preferred embodiments the offset arrangement arises since parts of the folding structure (e.g. the first part and second part, or similarly the frame and inclined beam) have different lengths between their mounting points on the fixed structure and the point where they connect together. This arrangement can aid folding since the larger length of one part may enable extra clearance during the folding operation.

Preferably the folding top structure does not provide any structural support for the pipe racker and other fixed drill equipment. The folding top structure preferably supports the weight of the top drive and drill string when in operation, but the fixed structure provides all the necessary support for the fixed drill equipment. As a result, it is not necessary for any disconnection or movement of the fixed drill equipment when the folding top structure is moved into the folding position.

In a preferred embodiment when in the erected position the top structure is used to support one or more of the crown block, top drive, travelling block, and/or upper parts of the guide rails. The folding operation may require some or all of the parts supported by the top structure to be removed. In a preferred embodiment the top structure is arranged such that in the folding operation the crown block remains connected to the top structure and moves with it to the folded position. The top structure may be arranged such that in the folding operation parts below the crown block should be removed.

The foldable top structure provides a mounting point for the main drilling line of the derrick apparatus when it is in the erected position. The drilling line extends downward through the derrick apparatus from the crown block on the upper part of the top structure. Preferably the derrick apparatus is also provided with one or more additional firing lines. There may be one additional firing line for double functionality, preferably two additional firing lines for triple functionality. The further functions for the additional firing line(s) may include blow out preventer (BOP) and marine riser building, building casing and/or working on the Christmas tree. The additional firing line(s) may be formed by structures extending away from the fixed structure so that the firing line(s) is/are outboard of the fixed structure. Alternatively, support structures for additional firing line(s) may be provided within the fixed structure. The casing line may be placed inside the fixed structure. In one preferred arrangement, a structure protrudes outwardly from an upper part of the fixed structure and forms a support for a secondary firing line as well as forming a mounting point for a part of the folding structure, preferably a mounting point for the connection of the inclined beam or second part to the fixed structure.

In a preferred embodiment an additional firing line is provided with an actuating mechanism, which may be a winch, and the actuating mechanism is also used to actuate the folding top structure.

The fixed structure preferably comprises an integrated drill floor. This enables the derrick apparatus to form a derrick having a unitary construction with an integrated design, wherein parts connected to the drill floor and to the derrick tower are designed together. Thus, the derrick apparatus is preferably a unitary structure comprising the derrick tower (for example the folding structure described above or the prismatic structure described below) in combination with the drill floor. In some preferred embodiments the derrick apparatus is a derrick for a drillship and the fixed structure is arranged for a direct connection to the structure of the ship. This advantageously results in a single unitary construction for direct connection to the ship. Conventionally, the drill floor is provided as a separate and independent part that connects to the drillship (or other platform), with the derrick being then mounted to the drill floor. By connecting a unitary derrick and drill floor arrangement directly to the ship it is possible to more efficiently design the derrick structure and also to manufacture the derrick and drill floor to a greater extent in a manufacturing facility away from the ship rather than needing to construct the derrick on board. The drillship (or rig) can hence be constructed much more quickly.

The drill floor may have a conventional arrangement of equipment. Preferably however the apparatus is arranged such that one or more parts normally on the drill floor are placed elsewhere, advantageously elevated above the drill floor, for example this may include utility winches, storage areas and/or drawworks.

The unitary structure can advantageously be tested prior to installation, including testing of drill equipment and other equipment installed on the tower and drill floor. In effect, it can be made as a ‘plug and play’ part for the ship.

The fixed structure may be constructed from beams, preferably with a void extending down the centre of the structure and across its internal width. Conventional framework derricks may have struts passing across internal parts of the derrick, which can reduce the opportunity to utilise the internal space.

Preferably, beams of the fixed structure extend vertically through the drill floor and support the drill floor. Thus, in contrast to conventional structures the upper tower part of the derrick apparatus is not supported on the drill floor. This means that the drill floor does not need to carry the weight of the tower, which may be 1500 tons or more, but instead need only carry the weight of the equipment mounted on the drill floor. Instead there is a unitary construction with beams that pass from beneath the drill floor, through the drill floor and extending above the drill floor, whereby the beams support the drill floor and also support the derrick tower. Preferably the beams form the main structural elements of the derrick tower.

In a particularly preferred embodiment, the fixed structure comprises a generally prismatic shape with a generally constant cross-section along the vertical extent of the fixed structure.

Thus, the cross-section at the top of the fixed structure where the foldable top structure is mounted may be substantially the same as the cross-section at the base of the fixed structure. This construction is advantageous since it creates a larger space within the structure extending up the full height of the structure. This is to be compared with conventional designs where the width of the structure tapers toward the top of the derrick.

The prismatic shape for the structure is of particular benefit when used in combination with a beam construction having a void across the internal width of the structure, since the extra space created by the shape is left open and can be easily used for any desired purpose, such as placement of equipment, running lifting lines for utility winches and the like, movement of drill string and riser sections, space for the drill string entry path and so on. Also, since the box beam may be hollow the vertical beams can advantageously be used to hold cabling, pipe work and the like, as well as preferably also a personnel elevator or any other access way. This hollow space also has the advantage that it may be cooled, or warmed-up and kept frost-free if required.

This arrangement is considered to be novel and inventive in its own right. The open structure provides increased visibility for the operator and this, in combination with the increased space for working, results in increased safety on the drill floor.

Therefore, viewed from a second aspect the invention provides a derrick apparatus for a drilling machine, the apparatus comprising a fixed structure for supporting drill equipment, wherein the fixed structure has a generally prismatic shape with a generally constant cross-section along the vertical extent of the fixed structure, and wherein the fixed structure comprises supporting beams about outer parts of the fixed structure and a void extending across the internal width of the fixed structure.

The arrangement of the second aspect may incorporate any or all features described in relation to the first aspect and preferred embodiments thereof. The second aspect may advantageously be used without the foldable top structure, for example for fixed offshore platforms or for land based drilling operations. The advantages of increased space within the derrick structure and of increased flexibility in installing and operating drilling equipment can be realised with or without the use of a foldable top structure.

The derrick apparatus of the second aspect is of particular benefit when used in combination with the integrated drill floor described above to thereby form a unitary derrick and drill floor apparatus. In a preferred embodiment this apparatus thus comprises supporting beams as described above that extend vertically through an integrated drill floor such that both the fixed structure (which advantageously forms a main part of the derrick tower and supports the fixed drill equipment) and the drill floor are supported by the beams, and the beams extend beneath the drill floor toward a base of the derrick apparatus. The supporting beams in this arrangement may be for connecting to a foundation structure to thereby mount the unitary derrick and drill floor apparatus on the foundation structure. The foundation structure may advantageously be the super-structure of a ship. The beams may be directly connected to the foundation structure.

A preferred arrangement for the generally prismatic structure has a rectangular cross-section (for example a square cross-section) such that the structure is generally cuboid. Although other cross-sections may have advantages the use of a four sided prism is considered to give the best opportunity for maximising internal space whilst also maximising the space for unobstructed openings through the sides of the structure.

The space at upper parts of the tower is increased using the prismatic shape and this permits the location of equipment to be varied compared to conventional towers, for example as explained above one or more parts normally on the drill floor may be placed elsewhere, advantageously elevated above the drill floor, for example this may include utility winches, storage areas and/or drawworks.

In a preferred embodiment the apparatus has a main drill line supported by the fixed structure. The drill line may be for holding a drill string from a crown block, with the drill line including a fastline extending from a drawworks to the crown block and a dead line extending from the crown block to a dead line anchor. The fast line and/or the deadline preferably pass outboard of the prismatic shape of the fixed structure. Thus, the drawworks and/or dead line anchor may be mounted outboard of the prismatic shape of the fixed structure. A pulley at an upper part of the fixed structure may be used to direct the drill line from an outer part of the fixed structure toward the crown block. Conventionally the main drill line runs within the tower structure, which can lead to problems with access and safety. The construction of this aspect allows for the drill line to be outside of the space enclosed by the tower, which places the lines further from zones where personnel operate.

Preferably hollow box beams form the main structural elements of the structure and are placed about the outer part of the structure. Where the structure has a rectangular cross-section the box beams may be placed at the corners of the rectangle. In preferred embodiments the box beams are hollow and provide pathways for cables and/or pipes. For example, the beams may provide pathways for heating, cooling or ventilation and/or for cables such as winch wires, for example for a lifting arrangement for a blow out preventer. Optionally and preferably a personnel elevator and/or an access way such as a stairway or ladder is installed in one of the box beams.

Enclosing pipe work and cabling within the beams protects from the weather and from sea water. This can hence help avoid corrosion and icing as well as avoiding excessively high or low temperatures that may adversely affect performance of equipment such as electrical or hydraulic equipment. Heating and/or cooling of the volume within the beams may be provided, for example to maintain the internal volume within a predetermined temperature range.

The use of a prismatic structure provides particular advantages when additional firing lines are required, since the supporting structures for the additional firing lines do not need to extend very far away from or inside of from the main structure before it is possible to access an unobstructed vertical line to the deck level and/or moon pool. Thus, in preferred embodiments the derrick apparatus comprises a main drill line along with one or more additional firing lines.

The derrick apparatus may be provided with a covering for use in protecting the derrick and/or drill equipment from extreme weather, in particular in arctic conditions. The covering may comprise a textile cover or plates for fitting between the box beam legs of the fixed structure. It will be appreciated that the simple shape of the main structure of this derrick makes it particularly easy to protect it from the weather in this way. Design, installation and removal are particularly easy. Instead of having many plates of different sizes and installation superstructure as known with the traditional “pyramidal” derricks, it may be sufficient to have only two types of plates for the preferred prismatic drilling tower, differing by their length (the tower is typically of rectangular section). This prismatic design would be especially adapted to the use of textiles—there may be only one piece or a very limited number of pieces of textile for each side of the tower. In addition, this prismatic shape opens for the design of foldable coverage. The textile sails might be designed so as to be folded/unfolded, for example, making use of principles used in sailing. Plates may be pulled together, or rolling curtains made of narrow plates may also be implemented. Moreover, when the protective covering is combined with the use of heating (or cooling) within the box beams, as discussed above, then it can be possible for additional protection to be provided since heat from the box beams may be retained within the covered derrick.

In further aspects, the present invention provides a method of operating a derrick apparatus comprising use of the derrick apparatus of the first or second aspect or any preferred arrangement thereof as described above.

The method may include folding a foldable top structure of the derrick, for example to permit passage of a marine vessel through a height restricted route.

In preferred embodiments, the method comprises lowering the top drive from the folding top structure, preferably by means of its guide rails. The top drive may then be secured above the drill floor. When guide rails are present, the method may include disconnecting the upper part of the guide rails and lowering the upper part of the guide rails, preferably with guidance from the remaining lower parts of the guide rails. The upper guide rails may then be secured above the top drive.

The folding structure may comprise a frame rotatably connected at a first point to a first side of the fixed structure with an inclined beam rotatably connected to the frame at a second point spaced away from the first point and the inclined beam releasably connected to the fixed structure at a third point spaced away from the second point and the first point. With this arrangement the method may include steps of releasing the inclined beam from the fixed structure and rotating the frame relative to the fixed structure to lower it toward the fixed structure and slide the inclined beam downwards. The folding operation may be controlled by a winch or gear mechanism arranged to lift the frame from the folded position toward the erected position.

In a yet further aspect the invention provides a method of manufacture of a derrick apparatus for a drilling machine, the method comprising: providing a fixed structure for supporting fixed drill equipment such as a pipe racker and providing a folding top structure having an erected position and a folded position, wherein when in the erected position the top structure is for supporting a top drive of the drilling machine and wherein at least a part of the top structure is arranged to fold around and/or beside the fixed drill equipment on the fixed structure such that when the top structure is in the folded position the height of the derrick may be reduced to the height of the fixed drill equipment without disturbing the fixed drill equipment.

In a still further aspect the invention provides a method of manufacture of a derrick apparatus for a drilling machine, the method comprising: providing a fixed structure for supporting drill equipment, wherein the fixed structure has a generally prismatic shape with a generally constant cross-section along the vertical extent of the fixed structure, and wherein the fixed structure comprises supporting beams about outer parts of the structure and a void extending across the internal width of the fixed structure.

The method of this aspect preferably comprises providing a unitary structure with a drill floor integrated with the fixed structure. This unitary structure may have features as described above. The method may comprise manufacture of the unitary structure at an onshore site followed by installation onto a vessel such as a drill ship. Preferably the method includes testing of the unitary structure and/or drill equipment installed on the structure prior to installation of the structure on the vessel.

Preferred features of the methods of manufacture may include providing features of the derrick apparatus as discussed above.

The folding structure of the invention is considered to provide benefits even when not folding fully down to the height of the fixed equipment. Thus, in another aspect the invention provides a derrick apparatus for drilling operations, the apparatus comprising: a fixed structure for supporting fixed drill equipment such as a pipe racker; and a folding top structure having an erected position and a folded position, wherein when in the erected position the top structure is for supporting a top drive drilling machine and wherein when the top structure is in the folded position the total height of the derrick apparatus is reduced and the folded top structure is arranged to apply a generally symmetrical load to the fixed structure, such that it can be supported by the fixed structure in the folded position without significant additional bending moment being applied to the fixed structure. This is advantageous since it avoids applying any abnormal loading to the fixed structure. When folded the loading is generally vertical and so the fixed structure can support the weight of the folded top structure in a similar manner to the way in which it supports the weight of the unfolded/erected top structure.

The apparatus of this aspect may incorporate any of the preferred features of the other aspects and apparatuses described above, either taken alone or in combination. Thus, the symmetrical loading may be achieved by use of a generally triangular folding structure, preferably a structure in which one part folds down across the fixed structure and one part is slid down to be supported at a side of the fixed structure.

In another alternative aspect the invention provides a derrick apparatus for drilling operations, the apparatus comprising: a fixed structure for supporting fixed drill equipment such as a pipe racker; and a folding top structure having an erected position and a folded position, wherein when in the erected position the top structure is for supporting a top drive drilling machine and wherein when the top structure is in the folded position the total height of the derrick apparatus is reduced and the top structure collapses around the fixed structure and reduces the total height of the derrick apparatus to about the height of the fixed structure. The use of such a folding structure provides an optimal reduction in height. Since the folding structure collapses around the fixed structure the additional height added to the height of the fixed structure by the folding structure in its folded position is minimal. The collapsed folding structure may be placed atop the fixed structure and/or beside the fixed structure. Preferably the folding structure comprises a first part that lies atop the fixed structure in the folded position and a second part that is located beside the fixed structure in the folded position. These parts may correspond to the first part and second part and/or to the frame and inclined beam described above.

The apparatus of this aspect may also or alternatively incorporate any of the other preferred features of the other aspects and apparatuses described above, either taken alone or in combination.

Preferably the folding structure comprises beams and is arranged such that in the folded position the folded structure fits on or around the fixed structure and increases the height of the fixed structure by no more than the width of the beams. By the use of a beam construction the additional height added to the height of the fixed structure by the folding structure in its folded position can be reduced to the beam width, even when the folded structure sits atop the fixed structure in the folded position.

A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a derrick and drilling equipment installed on a drillship and shown from the starboard side;

FIG. 2 shows the derrick of FIG. 1 from the port side;

FIG. 3 is a cut-away view with upper parts of the derrick omitted to show the drill floor equipment;

FIG. 4 is a side view from starboard illustrating the heights of parts of the derrick and associated equipment;

FIG. 5 shows the upper part of the derrick in expanded view, with the top structure of the derrick in its erected configuration;

FIG. 6 is a similar view and shows parts removed in preparation for the folding operation;

FIG. 7 shows the top structure of the derrick in a partially collapsed position;

FIG. 8 shows the fully folded, collapsed position, after the folding operation is completed; and

FIG. 9 is a side view from starboard illustrating the height of the top structure after folding is completed.

The derrick shown in the Figures is designed for mounting on a drillship such as the Ulstein X-Bow™ drillship variant. The basic design could of course be easily adapted for any drillship and also for other mobile drilling vessels such as semi-submersible or jack-up rigs. Certain features of the derrick of the preferred embodiment can also provide advantages when used for fixed drilling platforms and the like, as well as for land based drilling.

The design consists of two main parts:

1) The derrick structure, ranging from 2 metres above drill floor, with a “folding top” for passing under bridges and other obstacles; and

2) The drill floor with substructure, interfacing with ship at main deck level and positioning of all related equipment for riser tension, mux cable guide sheaves, hydraulic and booster line sheaves for hooking on to the marine riser. The diverter system and the mud return will also be a part of the substructure. Typically, the drill floor may be as low as 6 m above the ship's main deck, instead of 12-13 m for conventional design. One will appreciate the gains in weight of the structure, as well as in stability with a lower centre of gravity for the ship. The lowered height of the drill floor is brought about by the integrated design with the tower and drill floor being a single unitary structure and box beam legs of the fixed structure of the tower passing through and supporting the drill floor. This arrangement is described further below with reference to the drawings.

Drill equipment of the type supplied by National Oilwell Varco (NOV) of Norway has been used in the preferred embodiment, although it will be appreciated that the derrick could utilise any other suitable drill equipment. The design of the derrick provides a great deal of flexibility and space for installation of drill equipment and does not need specially designed drill equipment. In this preferred embodiment the equipment listed below is based on conventional drill equipment as supplied by NOV:

-   -   Hoisting winch for casing building     -   Drawworks     -   Drill line reel     -   Riser tensioners     -   Riser tensioner sheaves     -   Tension ring     -   Diverter, with riser assembly     -   Rotary table     -   Dead line anchor     -   Mousehole racking system     -   Elevated back-up tong     -   Service and access basket     -   Racking guide arm     -   Hydratong     -   Utility and manrider winches     -   Hydraracker, with guide racks and parking device     -   Fingerboards     -   Topdrive, with dolly     -   Travelling block     -   Crown block, with idler sheaves

Naturally, the location of the various equipments is governed by the derrick design. However, advantageously the equipment design and the interconnections between the drill equipment can be conventional. As a consequence there is no need for extensive retraining of the operating personnel. More detail of the drill equipment used in this example embodiment is given below.

As can be seen from the Figures, the derrick is a four legged box beam structure. The main derrick structure is a continuation of the drill floor and sub-structure, which fits directly on the ship main deck below. The box beams extend vertically through the drill floor and hence support the drill floor and also form the derrick tower structure. This is in contrast to conventional arrangements where the derrick tower is supported by the drill floor. This aids the structural strength of the drilling derrick and makes it an integrated part of the drillship. The drill floor with sub-structure and the derrick is designed to be fabricated as one complete and pre-commissioned unit.

FIGS. 1 and 2 show starboard and port side perspective views of the derrick. The Arrow marked FWD indicates the forward direction of the ship. In FIG. 1 the main equipment is shown as follows. The main firing line along the drill centre extends downward from the upper part of a foldable top structure. The foldable top structure is made up of an inclined A-frame 2 and an inclined sliding beam 4. Operation of the foldable top structure is explained below with reference to FIGS. 5 to 9. The top structure supports the degasser vent line 6, the crown block and water table 8. The top drive and travelling block 10 hang from the top structure along with upper parts of the guide rails 12.

The exemplary derrick is outfitted with standard and field-proven drilling equipment. The main feature of the derrick is a 1250 tonnes capacity top drive drilling machine, controlled by a heave compensated drawworks 24 located on a platform in the lower part of the derrick structure. The drawworks 24 is elevated above the drill floor. For handling of drill pipes the derrick is equipped with a NOV “Hydraracker” racking machine capable of handling 135 ft stands of drill pipe (3×45 ft). The upper guide track 14 for the pipe handling arms 16 of the Hydraracker is located at the top of the square box frame, where the square box frame terminates and where the foldable top structure begins. This is an important feature since the height of the upper guide track 14 and associated parts sets the maximum height for certain operations and in the drilling machine they are the uppermost parts that require extensive calibration and alignment. As explained below, the foldable top structure can fold down to below this height. This results in an optimal folded arrangement, since there is no need to disassemble the complicated and aligned parts of drilling equipment and yet the total height of the derrick can still be reduced right down to the height of the drilling equipment.

Fingerboards 18 for stacking of drill pipes and casing stands are located at elevations 15.7 and 33 meters above the drill floor. As shown in FIG. 2, utility and man-rider winches 20 are located on a platform at the opposite side of the upper fingerboard 18. The open box structure of the derrick legs enables integration of an elevator 22 inside one of the legs, along with piping and cables inside the legs.

At the base of the derrick, beneath the drill floor, riser tensioners 26 are fitted. Above the riser tensioners 26 a structure 28 holds the dead line anchor and drill line reel.

The derrick is designed with three firing lines. In addition to the main line in the drill centre, the derrick has a secondary firing line 30 at the forward end that can handle a blow out preventer (BOP) 32 and marine riser building and a tertiary firing line 34 at the aft end for casing building and working on the Christmas tree. From the secondary firing line 30 the BOP 32 and marine riser parts can be lowered into the moon pool and moved into the main drill line using a trolley. FIGS. 1 and 2 show, in dashed lines, operation of the secondary firing line 30 with a BOP 32. The tertiary firing line 34 includes a winch 36 than can advantageously also be used during folding of the top structure, as explained below.

FIG. 3 shows more detail of the drill floor in a cut-away view. The drill floor includes equipment such as the iron roughneck and elevated back-up tong 38, lower racking guide arm 40 and a rail-mounted service and access basket 42. The driller's cabin 44 is elevated and supported by the derrick structure. This gives a better overview for the operators and space below can be utilized for equipment. The drill floor will also be equipped with an automated mousehole racking system for connecting drill pipes. The riser tensioners 26 are supported off the sub-structure outside the drill floor.

The cut-away view of FIG. 3 also shows the cross-section of the four hollow box beams that form the main derrick structure. The personnel elevator 22 in the front starboard beam can be seen. The dimensions of the derrick box structures are as follows. The aft legs 48 have a depth of 1.4 meters and a width of 2.8 meters. The forward legs 50 have a depth of 2.1 meters and a width of 2.8 meters. The legs 48, 50 are positioned to match the frames of the ship so that the legs 48, 50 can be attached directly to the main ship structure. The beams for the inclined A-frame 2 and sliding beam 4 in the top structure have dimensions of 1.4×1.4 meters. In addition to the main steel, the derrick structure also includes bracings and wind walls.

The drill floor is 19.6×21.0 metres in this preferred embodiment. The available space on the drill floor is large since the width of the upper parts of the box frame means that utility winches and other parts can be located higher in the derrick structure instead of on the drill floor. Freeing up space on the drill floor in this way gives greater flexibility in the location of drill equipment and provides space for storage and so on.

The derrick can be assembled into a completed structure away from the drillship (or other mounting platform) and then installed on the drillship very easily by welding the derrick structure to the ship structure and making electrical and other connections (e.g. mud connections). This means that the assembled derrick can be tested away from the ship and hence ship-board testing is minimised. The same applies for drill equipment, which can be mounted on the derrick before the derrick is installed.

One of the main features of the derrick is the ability to lay down the top part in order to pass below the bridges such as the Bosporus Bridge for operating in the Black Sea and the Bridge of the Americas for traversing the Panama Canal.

The maximum allowed air draft from the waterline in order to safely pass below the Bosphorus Bridge at high tide is 58 meters. Vessels below this height can pass freely beneath the bridge. Vessels of heights of up to 62 metres can pass beneath the bridge with special arrangements and precautions. Other similar bridges have similar restrictions.

The highest fixed part of the derrick is the top of the Hydraracker at the upper guide track 14. The top structure is folded down to a height slightly below the Hydraracker as explained below. With the ship main deck 6.2 meters above the waterline (maximum draft of ship), the highest fixed part of the derrick will be 60.1 meters above the waterline. Hence, depending on draft and tide conditions the ship can pass the Bosphorus Bridge. It will also easily pass other bridges such as the Bridge of the Americas and the Suez Canal Bridge.

Details of the heights of various parts of the derrick are illustrated in FIG. 4. These example heights are based on installation of the exemplary derrick on the Ulstein X-Bow™ drillship. When fully erect, the top of the derrick is at a maximum height A, which is 76 metres from deck level. The top of the pipe racker 16 is at a height B of 53.9 metres. The upper fingerboard 18 is at a height C of 33 metres above the drill floor (39.4 metres above deck level) and the lower fingerboard 18 is at a height D of 15.7 metres above the drill floor (22.1 metres above deck level). Drawworks 24 and dead line anchor are at a height E, 13.4 metres above deck level and the drill floor is at F, 6.4 metres above the deck. The main deck, marked as height G is the datum for the heights above and it is 6.2 metres from the waterline height H at maximum draft.

The maximum allowed air draft for free passage at the Bosphorus Bridge is marked as M, and is 58 meters from the waterline as mentioned above.

Folding of the top structure will now be explained with reference to FIGS. 5 to 9. By folding to permit passage through height restricted shipping routes the derrick provides significant advantages compared to conventional ship-borne derricks. Typical known derricks might require a month in port to deconstruct and later reconstruct the structure of the derrick, and further time would be required after reconstruction in order to commission the drill equipment, perhaps 3 or 4 weeks. Hence the total time lost for a conventional derrick construction can approach 3 months. With the folding structure described herein there is no lengthy deconstruction or reconstruction and the folding can occur at sea if necessary. The folding operation can be completed in 2 or 3 days, at sea, and after the structure has been re-erected the commissioning time is minimal since the main drill equipment including the pipe racker is not disturbed by the folding and dismantling of the complex aligned and calibrated parts of the drilling machine is not necessary. The folding top structure consists of the A-frame 2 at the aft end and the inclined sliding support beam 4 at the front end. The A-frame 2 is attached to the derrick structure with hinged connections 52 on each side. The A-frame 2 and the inclined sliding beam 4 are hinged at the top, near to the crown block 8, while the sliding beam 4 is attached to the structure below with a removable locking pin at a locking pin joint 54. The structure of the locking pin joint 54 adjacent to the locking pin has a guiding mechanism such as a roller or rack and pinion arrangement for lowering of the sliding beam 4.

Before the top structure is folded the top drive 10 and the upper part of the guide rail 12 are removed. FIG. 6 shows the space created by the parts that are removed as indicated by the arrows X. The locking pin is also removed from the locking pin joint 54. The top drive 10 and the travelling block are lowered down towards the drill floor to a parking position where they are secured. The drill line is then disconnected and removed. For clarity the upper parts of the drill line are not shown in FIGS. 6 and 7, although the fastline and dead line are still shown. The drill line would be disconnected from the top drive 10 and travelling block during lowering of the top drive 10 and travelling block or after they have been parked at the drill floor. The upper part of the guide rail 12, with support structure, can then be disconnected and lowered to a parking position above the top drive 10, by use of the derrick utility winches. The upper part of the guide rail 12 will be guided onto the lower part of the guide rail 12 in order to secure the operation. The crown block 8 and the idler sheaves can stay in position on the water table.

The winch 36 for casing building at the aft end of the derrick is used for lowering and lifting of the derrick top structure. The winch 36 has a lifting capacity of 350 tonnes, while handling of the top structure requires approximately 125 tonnes of lifting capacity.

After the winch wire is attached and secured to the rear end of the A-frame 2 the locking pin on the sliding support beam 4 can be removed, and folding of the top structure can commence. When the A-frame 2 reaches the horizontal parking position it will be resting on cradles 56 on the port and starboard side of the structure.

The sliding beam 4 will slide through the guide mechanism and vertically down along the derrick structure until the A-frame 2 reaches the support cradles 56. When the folding operation is completed the sliding beam 4 is secured to the ship deck or to the main derrick structure, e.g. by wires.

The fully folded configuration is shown in FIG. 8 and also in side view in FIG. 9. From FIG. 9 it can clearly be seen that due to the design of the folding structure the maximum height of the derrick after folding is set by the height of the upper pipe racker 14 and not by the structural parts of the derrick. The A-frame 2, which still holds the crown block 8 is folded flat and sits beneath the height of the pipe racker 14. Since the sliding beam 4 is stowed outside of the derrick structure in the folded configuration it does not interfere with or require disassembly of the main drill equipment. Beneath the folded structure the lower parts of the guide rail 12 and other drill equipment remains intact and there is no need for deconstruction of these parts. Also, after folding it is possible to use the lifting capabilities provided by the secondary firing line 30 and tertiary firing line 34, if required.

For re-installation of the top structure the process described above will be reversed, with the winch 36 being used to lift the A-frame 2 and sliding beam 4 back into place. Once the locking pin is reinserted into the locking pin joint 54 the top drive and upper parts of the guide rail 12 can be reattached and the drilling machine can be made ready to use in a short period of time.

In a typical application, the derrick is installed on a deepwater drillship (12 000 ft. water depth) with a drilling hook load capacity of 1250 metric tonnes. By way of example, the capabilities of the derrick and drillship may be as follows:

-   -   The second firing line (BOP) has a capacity of 750 metric         tonnes. The casing building capacity is 350 metric tonnes.     -   Simultaneous drilling/under reaming and building of 20″ casing.     -   Marine riser building is separated from rotary table centre.     -   Capacity to operate with 1075 tonnes in the tubular setback at         drill floor level.     -   Heave compensated drawworks are used for the drilling operation.     -   The derrick can handle tubular stands of 135 ft length, similar         to a 210 ft derrick.     -   The folding design can quickly and easily reduce the height of         the derrick to the same height as the top of the Hydraracker         (pipe racker).     -   When the derrick top is folded down the drillship is able to         pass underneath the Bosporus, Panama Canal and Suez Canal         bridges.     -   The design is robust and simple, in order to require minimum         maintenance and inspection during its lifetime, compared with         conventional framework derricks.     -   The weight of the steel structure is similar or less than for a         conventional framework derrick.     -   Compliance with all international rules, regulations and         requirements for offshore drillships.     -   The derrick structure shall have a personnel lift installed in         one of the legs.     -   A subsea BOP stack (18¾″, 15.000 psi), with a marine riser of         21″ diameter and sections of 75′ lengths.

During drilling it will be possible to conduct the following operations simultaneously by use of the three firing lines:

1. Pulling of the marine riser with the pin-connector and perform testing of the BOP on the forward part of the derrick (750 tonnes lifting capacity) making up the marine riser and start running the BOP.

2. Building the casing string with the casing building equipment at the aft end of the derrick (350 tonnes lifting capacity).

3. Drilling operations with the main firing line.

The table below sets out further details of the main drill equipment used in the exemplary derrick arrangement:

Dry Weight Name Description (kg) Travelling Incl. in top drive (11500 kg), 7 sheaves Incl. In block 72″ for 2″ drilling line. top drive Top drive One top drive, 1250 t capacity, incl. block, 65 000 travelling gear/dolly. BOP handling Guiding system/dolly outside derrick 20 000 structure, incl. crown block and travelling block. (Crown and travelling: 20000 kg). Racking board Two level racking board (monkey board 42 100 33 m above drill floor and belly board 15.7 m above drill floor). (2 × 21050 kg). Pipe handling Two vertical column rackers with upper 66 000 and lower guide track. (Hydraracker IV). Standpipes Mud and cement (7500 psi and 15000 psi), 20 000 and hydraulic supply (230 bar). Crown block Clown block with fastline and idler 15 000 sheaves, for top drive. Winches Two manrider winches and three utility  5 580 winches, located in derrick structure. (840 kg × 2 and 1300 kg × 3). Lights Light fixtures in derrick, cables, trays etc. 10 000 Ladders and Access ladders and platform for operation, 10 000 platforms inspection and maintenance. Personnel Alimak rack and pinion lift, Ex approved.  8 000 lift Casing SAB-VT. Service & access basket on rails 17 685 stabbing (SWL 250 kg). Weight incl. guide rails board dolly and winch. Steel wire For Casing and BOP handling  7 500 HP hoses Mud rotary hose and cement hose  5 000 Powered For automated offline stand building 19 000 mousehole Drawworks 1250 ton heave compensated drawworks 100 000  Dead line 200 kps Dead line anchor.  4 300 anchor Drill line 2″ drill line of 7500 ft (2286 m). 29 000 reel & wire Iron One at well centre, one for offline 23 000 roughnecks standbuilding. Complete with travelling assembly. Catheads Incl. Two catheads and control system.  2 000 Rotary table RST 755 Rotary Support Table. Max 26 000 required static load: 1000 short ton. Local (LIR/LER). With drilling control and 19 000 Equipment monitoring system. Room Drillers cabin With drilling control and monitoring 10 000 system. Approx. 30 m2. HVAC HVAC for DCR & LIR.  1 000 Riser tensioner Complete with sheaves and utility 722 000  systems. QTY. 16. HP manifolds Manifolds for choke and kill, dual mud 39 000 standpipe and cement standpipe. Diverter Diverter assembly, with running and 21 000 test tool. Standbuilding ATWOOD 11, racking guide arm.  1 500 guide arm Elevated EBT-100-5  3 900 backup tong Casing standbuilding guide system Casing standbuilding winch Total weight: 1 312 565  

As noted above, a personnel lift/elevator 22 is installed inside the forward starboard leg for access to the levels where machinery that need inspection is located. Power cables, compressed air, hydraulic lines and high pressure mud are located in the forward port leg, and are used to supply the top drive through the flexible hose bundle. The derrick legs will not have equal cross sections, since the lift will require a larger cross sectional area than the other legs, and the leg designs are optimized for strength.

The personnel elevator will comply with the following norms and directives:

-   -   EN81:1-A2 (European Lift Directive)     -   DNV rules for certification of lifts (1987)     -   ATEX directive (94/9/EC)     -   EN 13463 (Mechanical EX protection)

Since the personnel elevator is located inside one of the legs it does not require any additional weather protection. The minimum shaft dimensions required are 1726×1590 mm. The elevator will have stops on six locations: ship main deck, drill floor, dead line anchor platform, lower fingerboard, upper fingerboard and one close to the top square section of the derrick.

It will be appreciated that various alternatives and modifications are possible whilst remaining within the scope of the invention as defined by the claims. In possible alternative embodiments instead of using the winch 36 for casing building to support the folding structure a separate winch or a gear arrangement could be used. The fore and aft placement of the secondary and tertiary firing lines could be reversed. For fixed platform and land based operations the derrick could be constructed with a fixed top structure, i.e. without the folding structure, whilst still providing advantages due to the shape and design of other aspects of the derrick. 

1. A derrick apparatus for a drilling machine, the apparatus comprising a fixed structure for supporting drill equipment, wherein the fixed structure has a generally prismatic shape with a generally constant cross-section along the vertical extent of the fixed structure, and wherein the fixed structure comprises supporting beams about outer parts of the fixed structure and a void extending across the internal width of the fixed structure.
 2. A derrick apparatus as claimed in claim 1 wherein at least one beam is hollow and generally vertically oriented, and wherein the vertical beam is used as a conduit for one or more of cabling, pipe work, access way and/or a personnel elevator.
 3. A derrick apparatus as claimed in claim 1, wherein the fixed structure comprises an integrated drill floor.
 4. A derrick apparatus as claimed in claim 1, wherein the derrick apparatus is a unitary structure comprising the fixed structure in combination with the integrated drill floor, whereby the derrick apparatus including the drill floor can be installed as a single unit.
 5. A derrick apparatus as claimed in claim 1 wherein supporting beams of the fixed structure extend vertically through an integrated drill floor such that both the fixed structure and the drill floor are supported by the beams, and the beams extend beneath the drill floor toward a base of the derrick apparatus.
 6. A derrick apparatus as claimed in claim 5, wherein the supporting beams are for connecting to a foundation structure to thereby mount the unitary derrick and drill floor apparatus on the foundation structure.
 7. A derrick apparatus as claimed in claim 1, wherein the derrick apparatus is a derrick for a drillship and the fixed structure is arranged for a direct connection to the structure of the ship.
 8. A derrick apparatus as claimed in claim 1, comprising a main drill line and one or more additional firing line(s).
 9. A derrick apparatus as claimed in claim 8, wherein the main drill line comprises a fastline running between the crown block and a drawworks and/or a dead line running between the crown block and dead line anchor passes and wherein the fastline and/or dead line is outboard of the prismatic shape of the fixed structure.
 10. A derrick apparatus as claimed in claim 8, wherein the additional firing line(s) are formed by or supported by structures extending away from the fixed structure so that the firing line(s) is/are outboard of prismatic shape of the fixed structure.
 11. A derrick apparatus as claimed in claim 1 comprising a folding top structure supported on the fixed structure and having an erected position and a folded position, wherein when in the erected position the top structure is for supporting a top drive drilling machine and wherein at least a part of the top structure is arranged to fold around and/or beside a part of the fixed drill equipment on the fixed structure such that when the top structure is in the folded position the height of the derrick may be reduced to the height of the fixed drill equipment without disturbing the fixed drill equipment.
 12. (canceled)
 13. A derrick apparatus as claimed in claim 11, wherein the folding structure comprises an arrangement of two or more hinged beams, for example box beams or girders, and wherein there is a void between two beams.
 14. A derrick apparatus as claimed in claim 11, wherein a void or multiple voids are used to provide space for parts of the folding structure, to enable the folding structure to move close to the fixed structure and/or to permit parts of the folding structure to be placed around or beside the fixed drill equipment.
 15. (canceled)
 16. A derrick apparatus as claimed in claim 11, wherein a part or part(s) of the folding structure are movably connected to the fixed structure at the height of the highest part of the fixed drill equipment or below that height and wherein the movable connection comprises a joint arranged for a sliding connection of the part of the folding structure relative to the fixed structure. 17-18. (canceled)
 19. A derrick apparatus as claimed in claim 11, wherein the folding top structure comprises a first part with a rotating connection to the fixed structure and a second part with a rotating connection to the first part and wherein, the second part is rotatably connected to the first part at a point spaced from the rotating connection of the first part to the fixed structure, and wherein the second part is releasably connected to the fixed structure at a point spaced from the rotating connection of the second part to the first part.
 20. (canceled)
 21. A derrick apparatus as claimed in claim 16, wherein the connection of the first part and the second part is at an upper location on the top structure when it is in the erected position and forms a mounting point for the crown block and/or for the top drive drill machine.
 22. A derrick apparatus as claimed in claim 19, wherein the folding structure is arranged such that when folded, the first part folds down around or beside a part of the fixed drill equipment and the second part is slid down beside the fixed structure.
 23. (canceled)
 24. A derrick apparatus as claimed in claim 11, wherein the folding top structure comprises a frame rotatably connected at a first point to a first side of the fixed structure with an inclined beam rotatably connected to the frame at a second point spaced away from the first point and the inclined beam releasably connected to the fixed structure at a third point spaced away from the second point and the first point.
 25. A derrick apparatus as claimed in claim 24, wherein the frame is an A-frame and preferably includes a void enabling it to fold over and about a part of the fixed drill equipment on the fixed structure.
 26. A derrick apparatus as claimed in claim 24, wherein the inclined beam slides down a side of the fixed structure when the folding structure is moved to its folded position.
 27. A derrick apparatus as claimed in claim 11, wherein the folding top structure provides an offset drill centre and is arranged such that the mounting point for the crown block and/or drill line is offset from the centre of the fixed structure.
 28. A derrick apparatus as claimed in of claim 11, wherein the folding top structure supports the weight of the top drive and drill string when in operation and/or wherein when in the erected position the top structure used to support the crown block and the top structure is arranged such that in the folding operation the crown block remains connected to the top structure and moves with it to the folded position. 29-40. (canceled)
 41. A method of manufacture of a derrick apparatus for a drilling machine, the method comprising: providing a fixed structure for supporting drill equipment, wherein the fixed structure has a generally prismatic shape with a generally constant cross-section along the vertical extent of the fixed structure, and wherein the fixed structure comprises supporting beams about outer parts of the fixed structure and a void extending across the internal width of the fixed structure.
 42. A method as claimed in claim 41 comprising providing a unitary structure with a drill floor integrated with the fixed structure.
 43. A method as claimed in claim 42 comprising manufacture of the unitary structure at an onshore site followed by installation of the unitary structure onto a vessel such as a drill ship. 44-46. (canceled) 